The invention relates to a piston and connecting rod for use in variable volume reciprocating machinery such as pumps, compressors and engines.
In an engine or pump of the type which uses reciprocating pistons, a major disadvantage of the standard piston is its weight. The reciprocating motion causes the piston to change direction often and suddenly and this places very large loads on the connecting rod, bearings and cylinder walls. The inertial forces on the connecting rod and the energy expended to accelerate and decelerate the piston throughout its cycle would be directly reduced by reducing the weight of the piston.
In addition, the connecting rod is subjected to the widest range of reciprocating stresses including compressive loads and the inertial forces from the piston changing directions. These stresses change many times per second. Some of these stresses are directly proportional to the weight of the piston and rod and the rate of change of the velocity. By decreasing the weight of the connecting rod and piston, the force required to change direction is directly decreased. Also, conventional connecting rods are short since they are connected to a lower part of the piston below the piston rings. This creates side forces on the cylinder walls as the connecting rod tilts substantially during the reciprocating motion of the piston in the cylinder.
Another major disadvantage of the standard piston is the need for piston rings to seal the space between the pistons and the cylinder walls. These rings have inherent problems in their design and function, including movement of the rings in their grooves as the piston changes directions. This causes the rings momentarily to lose their seal as the piston moves down the cylinder.
Also, piston rings have gaps which are necessary to mount them on the piston and to maintain tension against the cylinder walls for sealing. Pressure caused by the gases under pressure above the piston forces the gases through these gaps, reducing efficiency and, in engines, increasing emission of pollutants.
Also, the machining of a piston to accept rings and the manufacture of the rings and the labor necessary to install or replace them all increase the cost of conventional reciprocating piston machinery.
A standard piston is attached to the connecting rod by a wrist pin which adds considerable weight to the assembly and requires wrist pin bosses on the skirt or side walls of the piston. These bosses also add significant weight that contributes additional stress on the connecting rod.
The standard piston transfers a substantial amount of its heat to the cylinder walls through its piston rings and the lubricating oil. Very little heat is conveyed to the cylinder walls by the piston skirt. A standard piston skirt is usually made non-circular (out of round) through expensive machining to accommodate uneven expansion due to the need to have more material near the wrist pin bosses and less material away from the bosses.
Also, the drag produced as the piston slide on the cylinder walls causes frictional heating and loss of power. Other piston designs have been disclosed, but these have severe limitations associated with modifications to the cylinder walls, the crank pin, ball and socket joint, seals, complex machining and assembly requirements, and the like. (See, for example, U.S. Pat. Nos. 1,467,066; 2,023,466; 2,136,416; 2,284,645; 2,329,480; 2,710,137; 2,985,358; 3,078,033; 3,082,935; 3,523,001; 3,695,150; 3,716,310; 4,142,500; 4,178,899; 4,246,833; British Pat. No. 529,885; and French Pat. No. 1,133,388.